Abstract
The North Qilian Accretionary Belt, situated at the northernmost extent of the Proto-Tethys tectonic domain, preserves key tectonic events such as Proto-Tethys Ocean subduction and accretion. Despite ongoing debates about the closure mechanisms and timing of the North Qilian Ocean, our study presents novel findings on granitoids from the Changma region in the western segment of the North Qilian Accretionary Belt. Zircon U–Pb dating indicates an emplacement age of 436 Ma for the Qingshixia pluton and 425 Ma for the Heixialao pluton. The εHf(t) values of the Qingshixia granodiorite range from +8.25 to +10.89, with TDM2 model ages estimated between 614 and 716 Ma. In contrast, the εHf(t) values of the Heixialao monzogranite range from +1.79 to +4.48, with TDM2 model ages spanning from 1127 to 1291 Ma. The Qingshixia granodiorite displays adakitic traits, characterised by high Sr, low Y, low Yb, and a low K2O/Na2O ratio, whilst the Heixialao monzogranite exhibits peraluminous, high-potassium calc-alkaline features. The low concentrations of Ni and Cr, along with moderate Mg# values, suggest that the Qingshixia granodiorite likely originated from the partial melting of a subducting slab. By comparison with experimental melts, the relatively low Rb/Ba and Rb/Sr ratios and higher zircon saturation temperatures of Heixialao monzogranite suggest that it may have formed from partial melting of the mafic middle and lower crust. Integrating these findings with regional geological features and differences between east and west segments, we propose that the western segment of the North Qilian Ocean basin may have closed during the Late Silurian, contributing to a diachronic closure process from east to west and offering insights into the tectonic evolution of the Proto-Tethys Ocean.
Original language | English |
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Journal | Geological Journal |
Volume | online first |
DOIs | |
Publication status | E-pub ahead of print - 21 Nov 2024 |
Bibliographical note
Publisher Copyright:© 2024 John Wiley & Sons Ltd.
Funding
This work is supported by the National Natural Science Foundation of China (grants 42072260 and 42372253), the Youth Innovation Team of Shaanxi Universities, and the Natural Science Basic Research Programme of Shaanxi (program 2021JM-158).
Funders | Funder number |
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National Natural Science Foundation of China | |
Youth Innovation Team of Shaanxi Universities | |
Natural Science Basic Research Programme of Shaanxi | 2021JM-158 |
Not added | 42072260 |
Not added | 42372253 |
Keywords
- granitoids
- North Qilian
- petrogenesis
- Proto-Tethys
- Silurian